As the conductive part for electronic and electrical equipment described above, a Cu—Zn based alloy has been widely used in the related art, from a viewpoint of a balance between strength, workability (formability), and cost.
In a case of a terminal such as a connector, a material is used which is obtained by performing tin (Sn) plating on a surface of a base material (sheet) consisting of a Cu—Zn alloy, in order to improve reliability regarding contact with a conductive member of a partner side of the terminal. In a conductive part such as a connector which is obtained by performing Sn plating on a surface of a Cu—Zn alloy as a base material, a Cu—Zn—Sn based alloy may be used, in order to improve recycling efficiency of the Sn plated material and to improve strength.
Herein, for example, a conductive part for electronic and electrical equipment such as a connector is generally manufactured by a method which includes: obtaining a predetermined shape by performing punching on a thin sheet (rolled sheet) having a thickness of approximately 0.05 mm to 1.0 mm; and performing bending at least a part thereof. In this case, the connector is used such that the connector comes in contact with a conductive member of a partner side through the vicinity of the bended portion to acquire electric connection with the conductive member of the partner side and the contact state is maintained with the conductive material of the partner side by utilizing spring properties of the bended portion.
For a copper alloy for electronic and electrical equipment used in such a conductive part for an electronic and electrical equipment, excellent electrical conductivity, rollability, or punching formability is desired. In addition, as described above, in a case of the connector which is subjected to a bending process and is used to maintain the contact state with a conductive material of a partner side through the vicinity of the bended portion by utilizing spring properties of the bended portion, it is required that bending formability and stress relaxation resistance are excellent.
Therefore, Patent Documents 1 to 4 propose a method for improving stress relaxation resistance of the Cu—Zn—Sn based alloy.
Patent Document 1 discloses that it is possible to improve stress relaxation resistance by including Ni in a Cu—Zn—Sn based alloy and generating a Ni—P based compound, and addition of Fe is also effective in the improvement of stress relaxation resistance.
Patent Document 2 discloses that it is possible to improve strength, elasticity, and heat resistance by adding Ni and Fe with P to a Cu—Zn—Sn based alloy and generating a compound, and it is considered that the improvement of strength, elasticity, and heat resistance means improvement of stress relaxation resistance.
Patent Document 3 discloses that it is possible to improve stress relaxation resistance by adding Ni to a Cu—Zn—Sn based alloy and adjusting a ratio Ni/Sn to be in a specific range, and addition of small amount of Fe is also effective in the improvement of stress relaxation resistance.
Patent Document 4 aimed at (designed for) a lead frame discloses that it is possible to improve stress relaxation resistance by adding Ni and Fe with P to a Cu—Zn—Sn based alloy, adjusting an atomic ratio (Fe+Ni)/P to be in a range of 0.2 to 3, and generating a Fe—P based compound, a Ni—P based compound, and a Fe—Ni—P based compound.
However, recently, smaller and lightweight electronic and electrical equipment is required, and therefore, it is required that strength, bending formability, and stress relaxation resistance are further improved, in the copper alloy for electronic and electrical equipment used in the conductive part for an electronic and electrical equipment.
However, in Patent Documents 1 and 2, the amounts of Ni, Fe, and P were merely considered and it was difficult to reliably and sufficiently improve stress relaxation resistance by only adjusting the amounts thereof.
In addition, Patent Document 3 discloses the adjustment of the ratio Ni/Sn, but there was no consideration of a relationship between a P compound and stress relaxation resistance and it was difficult to sufficiently and reliably improve stress relaxation resistance.
Further, in Patent Document 4, the total amount of Fe, Ni, and P and the atomic ratio (Fe+Ni)/P were merely adjusted, and it was difficult to sufficiently improve the stress relaxation resistance.
As described above, it was difficult to sufficiently improve stress relaxation resistance of the Cu—Zn Sn based alloy by the method proposed in the related art. Accordingly, in the connector having the structure described above, residual stress is alleviated over time or in a high temperature environment; and thereby, a contact pressure against a conductive member of a partner side is not maintained, and a problem such as contact failure may occur early. In order to avoid such a problem, there was no choice in the related art but to increase a thickness of a material, and this caused an increase in the cost of a material and an increase in weight. Therefore, further reliable and sufficient improvement of stress relaxation resistance is strongly desired.
In addition, along additional miniaturization and light weighting of an electronic and electrical equipment, from a viewpoint of a yield of a material in a small terminal, a small terminal is formed by performing the bending so that an axis of bending is in a direction perpendicular to a rolling direction (Good Way: GW) and deformation is slightly applied to a direction of the axis of bending parallel to the rolling direction (Bad way: BW), and spring properties are ensured by a material strength TSTD which is measured by performing tensile test in the BW direction. Accordingly, excellent bending formability in the GW direction and high strength in the BW direction are acquired.